Grease composition



Patented Dec. 28, 1948 GREASE COMPOSITION Paul R. McCarthy, Allison Park, Pa.', assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application June 11,v 1947, .Serial No. 754,065

This invention relates to improved grease compositions, and in particular concerns grease compositions in which are combined good resistance to water-leaching and good mechanical and lubricating properties over a wide temperature range.

Greases suitable for general usev throughout the mechanical arts. as, for example, in lubricating wheel bearings, ball or roller bearings in light machinery, pump packing glands and the like, spindles, chassis and universal joints, etc should possess good resistance to. leaching by water or moisture combined with good mechanical characteristics at the moderately elevated temperatures often encountered in such applications. Among the mechanical characteristics desirable in such greases there may be mentioned: good chemical stability and mechanical adhesion, an A. S. T. M. dropping point of about 300 F. or higher, good bearing retention, and resistance to failure under load.

While it has been possible in the past to formulate grease compositions having good resistance to leaching by water, as well as compositions having desirable mechanical characteristics, attempts to combine these two properties have been unsuccessful since ingredients which promote leaching resistance detract from the desirable mechanical properties, and ingredients which improve the mechanical properties detract from the leaching resistance. For the most part, resistance to water leaching can be effected by including in grease compositions relatively large proportions of calcium base soaps, but such soaps adversely affect the mechanical characteristics. Alternatively,

.good mechanical properties can be secured through the use of sodium base soaps, but such soaps are Water-soluble and adversely affect leaching resistance.

It is accordingly an object of the present invention to provide grease compositions in which are combined the properties of resistance to. leaching by water and good mechanical characteristics.

A further object is to provide grease compositions resistant to leaching by water at temperatures up to the boiling point of water and having good mechanical characteristics throughout a wide temperature range including temperatures above the boiling point of Water.

Another object is to provide grease compositions having a wide range of general utility by reason of possessing properties requisite to a diversity of applications.

I have found that the above and related obiects may be realized in grease compositions com- 4 Claims. (Cl-..25236) prising a zinc fatty acid soap, an alkali-metal fatty acid soap, mineral or petroleum asphalt, and a viscous hydrocarbon oil combined in suitable proportions. More particularly, lhave found that compositions comprising from about to about per cent by weight of a mineral oil having a viscosity of 500-2000 S. U. V. at F., from about 10 to about 2.0 per cent by weight of asphalt, and from about 10 tov about 25 per cent by weight of a-mixture of zinc and alkali-metal fatty acid soaps in which the ratio. of alkali-metal fatty acid soap. to. zinc fatty acid soap is between about 3:1 and about 1:1,v display good resistance to leaching by water combined with the desirable mechanical and lubricating properties characteristic. of a good short fiber grease. The invention thus consists, in grease compositions comprising the enumerated ingredients in the critical proportions just given.

The. mineral oil ingredient in. the new rease compositions provided by the invention may be any refined or semi-refined parafiinic-, naphthene-, or asphalt base oil having a viscosity of about 500-2000 S. U. V. at 100 F; If desired, a blend of oils of suitable Viscosity may be employed instead of a single oil, and in a preferred embodiment of the invention the oil ingredient consists of about 2 parts by weight of a refined Mid-Continent. oil having a viscosity of about 500-520 S. U. V. at. 100 F; and about 1 part by weight. of an oil of similar origin having a. viscosity or about l9002000 S. U. V. at 100 F. Any desired viscosity within the operable. range of 500-2000 S. Tl. V. at 100 F. may be secured through suitable blending of diiferent oils in this manner.

The asphalt ingredient of the new grease. compositions may likewise be a. single product or a blend of difierent stocks so proportioned as to have the desired viscosity characteristics. It may be of mineral origin, or it may be a so-called petroleum asphalt such as is obtained in refining certain types of crude petroleum oils. Ordinarily, it is preferable to employ petroleum asphalt stocks or blends thereof having a. viscosity of about 200300 S. U. V. at. 210 F. in an amount representing between about 10 and about 20 per cent by weight of the entire composition depending upon the degree of Water resistance desired. In general, the degree of water resistance of the composition is proportional to the viscosity and the amount of the asphalt employed.

The zinc and alkali-metal soaps employed in the new compositions are soaps of fatty acids, such ass'tearic, palmitic, and oleicacids. Mixed 3 fatty acid soaps obtained by the saponification of animal and vegetable fats, and oils, such as tallow, lard, cottonseed oil, etc., may likewise be employed. Such soaps may be incorporated in the composition either individually or in admixture, or they may be formed in situ in accordance Wfith {usual grease-making procedure. In the final composition the combined'soap content is between about and 25 per cent by weight of the entire composition, and the ratio of alkalieral oil having a viscosity of about 1900 S. U. V.

metal soap to zinc soap should be maintained between about 3:1 and about 1:1, depending upon the degree of water resistance andthe dropping point desired.

In preparing a grease composition by forming the mixture of zinc and. alkali-metal fatty acid soaps in situ, a grease pressure kettle is usually. charged with about two-thirds of the mineral oil to be employed, the fatty acid and/or fatty acidcontainin material, zinc oxide, and an aqueous alkali-metal hydroxide, such as aqueous sodium or potassium hydroxide. The charge is then heated at a suitable saponification temperature and under autogenic pressure for about one hour. Under these conditions the alkali-metal hydroxide reacts with the fatty acid material and'when this reaction has gone to substantial completion the remaining fatty acid material reacts with the zinc oxide to form the zinc soap. Generally it is desirable to employ the zinc oxide in slight excess of the amount theoretically required to react with the fatty acid in order to avoid the occurrence of free acid in the grease. The saponification reaction is usually completed by heating in an open kettle, after which the remainder of the mineral oil and the asphalt is added, and the grease is milled and finished in the usual manner. The following examples will illustrate several ways in which the principle of the invention has been applied, but are not to be construed as limiting the same.

Example I Approximately 45.6 parts by weight of a refined mineral oil having a viscosity of about 500 S. U. V. at 100 F., 10.3 parts by weight of tallow, 4.8 parts by weight of stearic acid, 0.8 part by weight of zinc oxide, and 1.5 parts by weight of sodium hydroxide in the form of a 40 percent aqueous solution were charged into a pressure kettle and heated at 325-340" F. under a pressure of about 70-80 pounds gauge for about one hour. The contents of the kettle were then discharged into an open kettle and heated with stirring at about 260 F. for an additional two hours, after which 25.9 parts by weight of a refined mineral oil having a viscosity of about 1900 S. U. V. at 100 F. were added slowly with stirring- The mixture was allowed to cool to about 225 F. and 11.1 parts by weight of a petroleum asphalt stock having a viscosity of about 245 S. U. V. at 210 F. were added with stirring; after which the composition was cooled to l80200 F. and pumped into containers. hereinafter identified as grease A..'

Example II 4 charged into a pressure kettle and heated with stirring to a temperature of about 330 F. and under a pressure of about 90 pounds gauge over a period of about 1.5 hours. The mixture was held under these conditions for an additional 45 minutes, after which it was discharged into an open kettle.. Heating .with stirring was continued in'lthe open kettle at? a temperature of about 260-280" F. for 5 hours, 'Approximately 17.3 parts by weight of a refined minat 100 F. were then added to the kettle over a period of, one hour while the temperature fwasmaintained} at" about 280 F. The mixture was then allowed to cool to a temperature of about 250 F. During the preparation of the .sodium base stock as just described, a zinc base "s'tock'was prepared by charging a second pres- This composition is 5 sure kettle with 4.8 parts by weight of stearic acid, 0.81 part by weight of zinc oxide, 8.? parts by weight of the 1900 S. U. V. oil and 0.03 part by weight of water. This, mixture was heated with stiring to a temperature of about 1'75 Ffover a period of about' hour, and heating was continued at this temperature for an additional hour. The mixture was then discharged into an open kettle together with 8.7 parts by weight of the 1900 S. U. V. oil, and was dehydrated by heating at a temperatureof about 240 F. for an hour. The zinc base stock so prepared and 11.1 parts by weight of a petroleum asphalt stock having a viscosity of about 245 S. U. V. at 210 F. were thoroughly mixed with the sodium base stock at a temperature of about 250 F., after which the composition was filtered through steel wool and pumped into containers. This composition is hereinafter referred to as grease B.

,.The following Table I presents physicalnand performance data on each of the grease com- Per Cent Loss at F Per Cent Loss at F Per Cent Loss at F Per Cent Loss at 200 F. Bearing Test:

Grease Retention, Per Cent Grease Leakage, Per Cent Grease Thrown, Per Cent Oil Separation, Per Cent. Adhesion, Per Cent Loss...--

1 Navy Bureau of Ships ad Interim Specification 14L5lNT. v

In the above table, the bearing test referred to was carried out by subjecting aHoover No. 7404 ball bearing assembly filled with 5.5 grams of; the grease to 20-minute runs at each of the temperatures 80-'F.', 150 F., and 220 F. in a l3.v E. .C. grease testing apparatus. At the end of each run, weighings were made .to d'etermine the amount of grease retained in the bearing, the amount thrown out of the bearing by centrifugal force, and .the amount running out of the bearing race-way, i. e. the leakage. The figures presented represent an average of the three runs at different temperatures.

The oil separation test referred to in the table was carried out by filling a 1 /2 inch nickel filter con-e withthe grease and placing the cone in a .tared beaker. The beaker vand cone were placed in an oven maintained at a temperature of 150 F. for 48 hours, after which the beaker was weighed and the gain in weight calculated as per cent oil separation.

The adhesion test was carried out by filling a tared 1 /2 in. concave disc (center depressed 2% inch) with the grease and spinning it at 1750 R. P. M. for 3 minutes, after which the disc was weighed and the difference in weight calculated as per cent less.

It will be noted from the table that both of the grease compositions displayed the desirable mechanical characteristics of typical sodiumbase grease but at the same time had a high degree of resistance to leaching by Water even at temperatures approaching the boiling point of Water.

In order to demonstrate the effect of varying the relative amounts of sodium and zinc soaps in the new compositions, a number of different compositions were prepared as described above in Example II and were subjected to the leaching test. The composition of these greases and their degree of resistance to leaching as well as consistencies and dropping points are summarized in Table II:

Table II Composition I aroo wwoa Hugo 4000C normwousooooo It will be noted from the above data that while compositions I and II containing relatively high ratios of sodium soap to zinc soap have consistency values and dropping points within the range desirable for a general purpose grease, they are unduly subject to leaching by water and are hence unsuited for many purposes. Compositions HI and IV, which contain lower ratios of sodium soap to zinc soap, however, have good resistance to leaching by water even at relatively high temperatures and at the same time retain to a large extent the desirable consistency and dropping point characteristics of compositions I and II. As a result of experiments similar to those summarized in the table, it has been determined that grease compositions of the present type in which the ratio of sodium soap to zinc soap is greater than about 3:1 are not satisfactorily resistant to leaching by water, whereas those in which said ratio is less than about 1:1 are too soft and lowmelting for general applicability.

The improved grease compositions provided by the invention are suitable for use in a wide variety of applications, particularly those in which good performance at moderately high temperatures is a requisite. They are especially adapted for use in lubricating moving parts which are exposed to the weather, i. e., farm machinery, donkey engines, cable systems, chassis joints, etc., since they combine good resistance to water leaching with satisfactory mechanical performance.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the methods or ingredients employed provided the products stated by any of the following claims he obtained.

I, therefore, particularly point out and distinctly claim as my invention:

1. An improved grease composition comprising between about 55 and about per cent by Weight of a refined mineral oil having a viscosity between about 500 and about 2000 S, U. V. at F., between about 10 and about 20 per cent by weight of asphalt, and between about .0 and about 25 per cent by weight of a mixture of a1l ali-metal and zinc fatty acid soaps, the ratio of alkali-metal soap to zinc soap being between about 3:1 and about 1:1.

2. An improved grease composition comprising between about 55 and about 80 per cent by weight of a refined mineral oil having a viscosity between about 500 and about 2000 S. U. V. at 100? F., between about 10 and about 20 per cent by weight of asphalt and between about 10 and about 25 per cent by weight of sodium and zinc fatty acid soaps, the ratio of sodium soap to zinc soap being between about 3:1 and about 1:1.

3. An improved grease composition comprising between about 55 and about 80 per cent by weight of a refined mineral oil having a viscosity between about 500 and about 2000 S. U. V. at 100 F., between about 10 and about 20 per cent by Weight of petroleum asphalt having a viscosity between about 200 and about 300 S. U. V. at 210 F., and between about 10 and about 25 per cent by weight of sodium and zinc fatty acid soaps, the ratio of sodium soap to zinc soap being about 2:1.

4. An improved grease composition comprising approximately 45.0 per cent by weight of a refined mineral oil having a viscosity of about 500 S. U. V. at 100 F., approximately 28.8 per cent by weight of a refined mineral oil having a viscosity of about 1900 S. U. V. at 100 F., approximately 10.8 per cent by weight of sodium tallow soap, approximately 5.4 per cent by weight of zinc stearate soap, and approximately 10.0 per cent by weight of petroleum asphalt stock having a viscosity of about 245 S. U. V. at 210 F.

PAUL R. MCCARTHY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Lubricating Greases, by Klemgard (1937 edition), pages 39, 680 and 681. 

